Prior known temperature sensors such as thermocouples have included a heavy steel tube with a pair of solid dissimilar metal wires running the length of the tube, and a hard fired ceramic insulator which separates the wires and keeps them from contacting the inside of the tube. The insulator has an outside diameter which permits it to slide easily within the metal tube and two lengthwise bores, one to accommodate each of the wires. The firing (baking) of the insulator makes the insulator hard and brittle. Also, it is known to crimp the tip of the tube onto the ends of the wires to form the thermocouple junction.
The prior art thermocouples have several drawbacks for certain uses. First, the hard fired ceramic insulator is subject to damage from vibration or impact, which may occur, for example, when these thermocouples are used to measure temperatures in foundries and other harsh work environments. In order to make the temperature sensors stronger, the walls of the metal tube which surrounds the insulator have been made thick. The tube wall thickness and the brittle insulator each make it impossible to bend the thermocouple, which may be necessary in order to measure the temperature of certain areas.
The use of solid metal wires can also be a drawback. Generally the solid wires must be connected to flexible, stranded conductors which in turn are connected to the necessary measuring junction. The connections between the solid and flexible conductors are possible points of failure in the system. For increased mechanical strength, the connections may be potted. The potting material may be the component with the lowest temperature rating of the entire sensor, and thus may limit the maximum temperature to which the sensor can be exposed safely.